For the production of polyolefins, the trend is to use mass polymerization processes instead of solution processes. With a mass polymerization process, there is little or no cleaning or “deashing” of the final polymer, thus substantial amounts of catalyst residue are left in the polymer. This is especially the case in the production of polypropylene by the so called SPHERIPOL process, where the polymer is typically deashed only with water. While this process is adequate for homopolymers due to the high porosity of the polymer grains, it is inadequate for copolymers of polypropylene where the polymer is no longer porous due to the rubber phase filling in the cavities of the resin. Thus, in the case of many polypropylene resins, especially copolymers of polypropylene, there is a significant catalyst residue left in the polymer.
Catalyst resides left behind in polyolefin materials are a problem given that, among other reasons, the catalysts are often activated by light. This light activation causes the breakdown of the polymer and results in a loss of properties and discoloration. While there have been some disclosures of using stabilizing compounds such as hindered amines or phenolic compounds to stabilize polymers against UV degradation, such measures are often inadequate. For further background, see, U.S. Pat. Nos. 6,329,465 B1; 6,284,822; 6,231,936 B1; 6,013,723; 5,877,260; 5,455,289; 5,132,344; 4,708,979; 4,692,486; EP 0 984 037 A1; EP 0 341 925 B1; and JP2001-200069. In fact, it is known that some antioxidants such as phenolic antioxidants act antagonistically, or unfavorably, with other additives such as, for example, hindered amine additives. (See, e.g., PLASTICS ADDITIVES 438-439 (Geoffrey Pritchard ed., Chapman & Hall 1998).
What is needed is a polyolefin composition that is UV radiation stable such that it is suitable for articles of manufacture exposed to light, such as automotive parts. While ethoxylated amines have been used as antistatic agents, such as disclosed in, for example, U.S. Pat. No. 5,455,289, and in PLASTICS ADDITIVES 112 (1998), the present invention is directed to the surprising discovery that ethoxylated amines act synergistically with other stabilizing agents to improve the UV stability of polyolefin compositions.